The Lord Jesus said this about the great tribulation which will come upon Jerusalem in the future:
"For then shall be great tribulation, such as was not since the beginning of the world to this time, no, nor ever shall be. And except those days should be shortened, there should no flesh be saved: but for the elect's sake those days shall be shortened" (Mt.24:21-22).
This is exactly how the great tribulation will be shortened:
"I will gather all the nations to Jerusalem to fight against it; the city will be captured, the houses ransacked, and the women raped. Half of the city will go into exile, but the rest of the people will not be taken from the city. Then the Lord will go out and fight against those nations, as he fights on a day of battle. On that day his feet will stand on the Mount of Olives, east of Jerusalem" (Zech.14:2-4).
The eschatology of the preterists has no place for the fulfillment of this prophecy. So you must think that it has already happened. When did it happen?